Avoriaz is only around a 1h30 - 1h45 drive from Geneva Airport. You could hire a car, but with so many transfer companies running shuttles to the resort, why not take it easy and let someone else do the work?
With an airport transfer:
you’ll often be dropped right at your door
you’ll save money over the cost of a hire car
you normally won’t have to wait long at the airport to be picked up